Systems for manufacturing commercial products of rare earth magnet include a single part system wherein a part of substantially the same shape as the product is produced at the stage of pressing, and a multiple part system wherein once a large block is shaped, it is divided into a plurality of parts by machining. In the single part system, a pressed part, a sintered or heat treated part, and a finished part (or product) are substantially identical in shape and size. Insofar as normal sintering is performed, a sintered part of near net shape is obtained, and the load of the finishing step is relatively low. However, when it is desired to manufacture parts of small size or parts having a reduced thickness in magnetization direction, the sequence of pressing and sintering is difficult to form sintered parts of normal shape, leading to a lowering of manufacturing yield, and at worst, such parts cannot be formed.
In contrast, the multiple part system eliminates the above-mentioned problems and allows pressing and sintering or heat treating steps to be performed with high productivity and versatility. It now becomes the mainstream of rare earth magnet manufacture. In the multiple part system, a pressed block and a sintered or heat treated block are substantially identical in shape and size, but the subsequent finishing step requires cutting or grinding. It is the key for manufacture of finished parts how to cut, grind or otherwise machine the block in the most efficient and least wasteful manner.
For the machining of rare earth magnet blocks, outer-blade cutoff wheels (in the form of a diamond wheel having diamond abrasives bonded to an outer periphery of a disk) are generally used as well as grinding wheels.
When a rare earth magnet block is cutoff machined by such wheels, the magnet block is generally secured to a carbon-based support by bonding with wax or a similar adhesive which can be removed after cutting. The bonding with wax is achieved by heating the carbon-based support and the magnet block, applying molten wax between the support and the magnet block, and cooling for solidification. In this state, the magnet block is cut into pieces. After the cutting operation, heat is applied to melt the wax, allowing the magnet pieces to be removed from the support. Since wax is kept attached to the magnet pieces at this point, the wax must be removed using a solvent or the like.
The adhesive way of securing a magnet block with wax involves concomitant steps of heat bonding, heat stripping and cleaning in addition to the cutting step. This renders the process very cumbersome and adds to the cost of the cutting process. Insufficient securement may exacerbate the accuracy of cutting and allow for chipping during the cutting operation.
Patent Documents 1 and 2 disclose jigs for holding a magnet block or workpiece without a need for adhesion. These jigs are configured to clamp the workpiece utilizing the elasticity of rubber or resin. As alluded to previously, magnet machining starts with a magnet block as sintered. Since the dimensional accuracy of a sintered magnet block is affected by the powder density and pressure during pressing prior to sintering and the atmosphere and temperature during sintering, the block has noticeable dimensional variations. To tightly hold such a block without adhesion, the jigs utilizing deformation of elastic members as in Patent Documents 1 and 2 are effective. However, there still remain problems including allowance for movement during cutting operation owing to elasticity and degradation of elastic members. Then the problems of chipping and dimensional accuracy are not fully solved.